PROJECT SUMMARY/ABSTRACT Periodontitis affects nearly half of the adult US population and two-thirds of adults are overweight or obese. Overweight and obesity increase the risk of periodontal disease incidence and progression as well as comorbidities such as diabetes and metabolic syndrome that are strongly associated with periodontal disease risk. It is clear from the medical literature that obese persons incur more total costs for medical care, including inpatient stays, outpatient visits, diagnostic procedures, and prescription drugs than non-obese. However, data regarding adverse effects of overweight and obesity on periodontal outcomes and the excess costs they may impose on routine periodontal care are lacking. This study is a retrospective cohort study of 7,300 new periodontal patients at a large urban dental school clinic whose demographic and clinical data are housed in a data repository. The primary exposure, obesity or overweight status will be determined from heights and weights reported on a medical history screening form. Data on periodontal treatments performed and outcome measures on each tooth (probing depth, attachment loss, plaque score, tooth retention) have been recorded. We will quantify and compare periodontal disease treatment types (surgical, non-surgical, antimicrobial), frequency, clinical outcomes and costs among patients who are obese, overweight and normal weight. The results of this study will fill in gaps in our knowledge concerning the contributions of overweight and obesity to parameters of routine treatment of periodontal disease. 1